Abrasive wheels are generally formed by bonding together abrasive grains or particles with a bonding material, typically a resin. Such wheels are employed in grinding operations. For example, “thin” wheels are used in cutoff and snagging operations and may be used without external cooling. Thin abrasive wheels may have no reinforcement or they may be fabric or filament reinforced. Thin abrasive wheels can have full or partial (zone) reinforcement.
Both flat and depressed center abrasive wheels are available. Flat (Type 1) wheels typically are held between two flanges of equal size and mounted on the rotating spindle of a machine.
Depressed center abrasive wheels are characterized by a displacement of the central portion (or the hub) of the wheel with respect to the periphery of the wheel. One face of the wheel has a depressed central portion, while the other face exhibits a raised center. Classified as Type 27 or Type 28, these wheels can be used for cutting or grinding.
Generally, depressed center wheels are mounted on angle machines between two flanges: a rear flange, facing the raised central portion or the raised hub of the wheel, and a front flange. While the front flange fits entirely within the depressed center, the back flange typically covers the raised center and extends beyond it onto the flat portion of the wheel.
Hub assemblies hold the wheel between the two flanges for mounting it onto the spindle of a grinding machine. Often, a hub assembly has two parts, each generally corresponding to the rear and front flange, and are held together by a threaded nut. In another hub assembly design, the two pieces are bonded to the wheel by using an epoxy resin. A one-piece hub assembly which is integrally molded to the wheel has also been developed. In some cases, the mounting assemblies are sufficiently inexpensive to allow discarding the mounting hub along with the worn-out wheel.
Since abrasive wheels are operated at high rotational speeds and used against hard materials such as steel and other metals, masonry or concrete, they must be capable of withstanding these conditions and of operating safely. Furthermore, since they wear out and need to be replaced, keeping their cost of manufacturing low is also important. Because maximum stress occurs at or near the center of the hub, the hub portion of the wheel usually contains additional reinforcing material, typically one or more circles of fiberglass cloth extending approximately to the juncture of the hub and the grinding face of the wheel. Typically, about one-third of the fiberglass cloth is wasted in cutting these circles.
Therefore, a need exists for safe abrasive wheel assemblies and for lowering their manufacturing costs.